The present disclosure relates to optical communication systems and more particularly to systems and methods for handling failures in optical communication networks.
In order to accommodate increasing demands from Internet traffic, optical communication links are evolving to carry higher and higher data rates over greater and greater distances. Wavelength division multiplexed (WDM) links are carrying greater numbers of more densely spaced channels on the same fiber. For example, a single optical fiber may carry 160 channels, each having a data carrying capacity of 10 Gbps, making for a total available capacity of 1.6 terabits per second. Roughly speaking, this is the information equivalent of more than 19 million simultaneous phone calls.
Advances in optical amplifier technology allow such high capacity links to extend for thousands of kilometers. By traversing oceans and spanning continents with high capacity links, a broadband backbone network of global reach is being constructed.
With such a large volume of Internet traffic depending on the operational status of a single WDM link, assuring link reliability is of paramount importance. Many protection schemes have been developed to assure fault tolerance. In the dominant fault tolerance paradigm, when a link failure is detected optical signals are redirected through an alternative route that avoids the failed link. The alternative routes are pre-configured. In some cases, the optical hardware is arranged such that the same optical signal flows down a working route and a redundant protection route simultaneously with the receiver selecting the protection route upon detection of a failure. In other implementations, the protection route is traversed by the protected signal only upon a link failure and is otherwise available to carry low priority traffic that may be left unprotected.
This fault protection paradigm, often referred to as the “1+1” protection scheme, assumes that the backup link(s) will not fail before the protected primary link has been repaired. A reliability problem thus arises where links traverse a substantially inaccessible region such as a body of water. If, for example, a transoceanic link goes down due to an optical amplifier failure or a simple cable break thousands of miles from shore, repairs may require days or even weeks. If any portion of the backup link fails in the interim, the protected traffic will lose service, causing disruption and loss of revenue to the service provider.
What is needed are systems and methods for providing robust fault tolerance to optical communication links that traverse substantially inaccessible regions and therefore require tolerance to multiple failures.